Night sweats and a fever at night can leave you uncomfortable and confused about what your body is trying to tell you. Night fevers often happen because your body’s temperature naturally rises in the evening and reacts to infections or inflammation more strongly at that time. This pattern can make a mild daytime fever feel worse once the sun goes down.

Your immune system works differently throughout the day, which can cause temperature spikes after dark. Infections such as colds, flu, or more serious illnesses may lead to this pattern. Other possible causes include autoimmune conditions, medication side effects, or even certain cancers. In many cases, experiencing fever at night can be the body’s way of signaling that it’s fighting off an infection or responding to inflammation.

Understanding why your body heats up at night helps you decide when to rest, when to monitor symptoms, and when to see a doctor. Paying attention to how long the fever lasts and other symptoms that appear with it can guide you toward the right care.

Key Takeaways

• Night fevers often reflect your body’s natural temperature cycle and immune response.
• Infections, autoimmune diseases, and some cancers can cause recurring nighttime fevers.
• Tracking symptoms and duration helps decide if medical attention is needed.

Primary Causes of Night Fevers

Your body temperature can rise at night for several reasons. Infections, immune system activity, and reactions to certain medicines often explain these temperature changes. Each cause affects how your body regulates heat and responds to illness or stress.

Infections and Viral Illnesses

Infections are the most common cause of night fevers. Your immune system fights viruses and bacteria more actively during rest, which can raise body temperature. This natural response helps your body slow the growth of harmful organisms.

Respiratory infections, such as the flu or pneumonia, often cause nighttime temperature spikes. Tuberculosis and urinary tract infections can also lead to fevers that appear or worsen after sunset.

You may notice chills, sweating, or fatigue along with the fever. These symptoms reflect your body’s effort to fight infection. If a fever lasts more than three days or reaches high levels, you should contact a healthcare provider to rule out serious illness.

Autoimmune Disorders

Autoimmune disorders can cause your body to produce fevers even without infection. In these conditions, your immune system attacks healthy tissues, which triggers inflammation and heat production.

Diseases such as lupus, rheumatoid arthritis, and inflammatory bowel disease often lead to mild but persistent fevers. These fevers may rise at night because hormone levels and immune activity shift during sleep.

You might also feel joint pain, stiffness, or fatigue. These signs can help doctors identify an underlying autoimmune problem. If you experience night fevers along with these symptoms, medical testing can help confirm the diagnosis and guide treatment.

Medication Reactions

Some prescription and over-the-counter medicines can cause fevers as a side effect. This reaction may occur because your body sees the drug as a foreign substance and activates immune defenses.

Antibiotics, blood pressure medicines, and certain anti-seizure drugs are known to cause this effect. The fever may appear after several doses or only at night due to your body’s natural rhythm.

If you suspect a medicine-related fever, write down the timing, dose, and symptoms. Share this information with your doctor before stopping the drug. Adjusting the medication or switching to another may resolve the fever safely.

Other Contributing Factors to Nighttime Fever

Several internal and external factors can raise your body temperature after dark. Hormonal changes, ongoing medical conditions, and environmental influences each play a role in how your body reacts to infection or stress during sleep.

Hormonal Imbalances

Your hormones help regulate body temperature throughout the day. At night, natural shifts in cortisol and melatonin can affect how your body controls heat. Lower cortisol levels may allow more inflammation, which can raise temperature. Meanwhile, melatonin can slightly increase warmth as your body prepares for rest.

Thyroid disorders also influence nighttime temperature. Hyperthyroidism often causes heat intolerance and sweating, while hypothyroidism can make you feel cold but sometimes lead to unstable temperature control.

Fluctuations in sex hormones—such as estrogen and progesterone—may also cause nighttime temperature swings. Many women notice mild fevers or hot flashes during menstrual cycles or menopause. These changes usually reflect hormone shifts rather than infection but can still disturb sleep.

Chronic Medical Conditions

Certain long-term illnesses can cause fevers that appear more noticeable at night. Autoimmune diseases, such as lupus or rheumatoid arthritis, often create inflammation that peaks during rest. The immune system tends to act more aggressively overnight, which can make symptoms worse.

Infections that persist, like tuberculosis or endocarditis, may also cause recurring fevers that rise after sunset. These conditions often develop slowly, and the pattern of nighttime fever can help doctors identify them.

Some cancers, including lymphoma, can trigger night sweats and low-grade fevers. The body reacts to abnormal cell activity by releasing inflammatory chemicals, which raise temperature. If you experience this pattern for several days, medical evaluation becomes important.

Environmental and Lifestyle Influences

Your surroundings can easily affect body heat at night. A warm bedroom, heavy blankets, or poor ventilation can trap heat and make a mild fever feel worse. Adjusting room temperature or bedding often helps reduce discomfort.

Stress and anxiety may also raise nighttime temperature. The body releases stress hormones that temporarily increase metabolism and warmth. Over time, this can mimic mild fever symptoms.

Late meals, alcohol, or caffeine before bed can interfere with your body’s cooling process. Light exercise earlier in the day usually supports better temperature control, but intense workouts right before sleep may cause temporary heat buildup.